Hi:
Pull-down menus are implemented in HTML (usually) as HTML forms. The pull-down list is a select box and then when the user makes their selection, the item they select gets posted with the form action.
From other posts you've made, I remember that you are working in an EG and possibly also BI server environment. If you are working with the BI Platform, the SAS/IntrNet examples mostly correspond to what you can implement with the SAS Information Delivery Portal. The Stored Process Web Application (SPWA) is another way that you could create a custom front end and then build whatever kind of prompting interface you want, you would invoke your stored process via URL making a call to the SPWA to execute the stored process.
If you want to implement pull-down menus with EG, you should investigate the Enterprise Guide Parameter Manager -- which lets you define parameters (such as procedure options or task/wizard options) and then the Parameter interface automatically will prompt the user with a pull-down menu when they run a project in which the Parameter Manager was used to define parameters.
Other methods of creating pull-down menus, specifically in EG, involve the use interfaces programmed using methods other than HTML forms generally using custom tasks written in VB.NET or C#.
cynthia